The synaptic, neuronal and neural network mechanisms driving anxiety-like behaviors are not completely understood. Transient Receptor Potential channels (TRPC), belonging to the TRPC1/4/5 subfamily, are abundant in the brain areas implicated in control of innate fear responses, including the amygdala and the bed nucleus of the stria terminalis (BNST). Consistent with this expression pattern, we found recently that specific TRPC subunits belonging to this subfamily may contribute to anxiety mechanisms, possibly modulating the signal flow within specific neural circuits in the brain through activation of Gaq/11 protein-coupled receptors (specifically, Group I mGluR and CCK2 receptors). However, TRPC4 and TRPC5 subunits (members of the TRPC1/4/5 subfamily) can either form homomeric channels or heteromerize with the TRPC1 subunit, resulting in heterotetrameric TRPC channels with distinct biophysical and functional properties. These TRPCs can differentially regulate neuronal functions and, possibly, anxiety states, depending on their subunit composition. Combining genetic, behavioral, electrophysiological and optogenetic tools, we will explore the functional roles of distinct TRPC subunits and their combinations in structural components of the anxiety circuitry-the amygdala and BNST-and their contribution to control of anxiety-like behavioral responses. In our experiments, we will focus on the behavioral and functional analysis of mice lacking TRPC1, TRPC4 and TRPC5 (and combinations thereof) subunits. We will also study TrpC floxed mice in which TRPC subunits will be ablated specifically in subdivisions of the amygdala or BNST. In Aim 1, we will explore the roles of TRPC1/4/5 subfamily of TRPC channels in anxiety-like behaviors by probing anxiety levels in mice lacking different combinations of TRPC subunits. We will also investigate the effect of different TRPCs' ablation on synaptic functions, Gaq/11 protein-mediated signaling and neuronal spike output in intra-amygdala projections. We will then explore the role of TRPC channels in the function of local neuronal circuits in the amygdala (Aim 2). Specifically, we will examine whether the balance between excitation and inhibition in interdivisional projections in the amygdala is affected in neurons and interneurons in mutant mice. Finally (Aim 3), we will investigate the role of TRPC channels in regulation of synaptic and neuronal functions in the BNST, focusing on its two different subregions, the oval nucleus and anterodorsal BNST, known to exert opposing effects on anxiety. We will use optogenetic tools to achieve projection-specific activation of the fibers arising in the BLA and terminating in the BNST. We hypothesize that the ablation of TRPC1/4/5 subunits may modify the signal flow in the amygdala-BNST circuits, leading to the enhanced activation of adBNST and resulting in diminished anxiety-like responses, as adBNST activation was shown to be anxiolytic. These studies, illuminating the role of TRPC channels in anxiety-related behavioral processes, may contribute to our better understanding of how anxiety is regulated at the level of interacting components of the corresponding brain circuits.